1. Field of the Invention
The present invention relates to a lithium rechargeable battery. In particular, the present invention relates to a lithium rechargeable battery having an improved electrolyte injection structure.
2. Description of the Prior Art
Based on the trend towards compact and lightweight portable electronic appliances, batteries having a small size and high capacity have become increasingly necessary as the power source for driving the appliances. In particular, lithium rechargeable batteries have an operating voltage of 3.6V, which is three times higher than that of nickel-hydrogen batteries or nickel-cadmium batteries widely used as the power supply of portable electronic appliances, as well as a high energy density per unit weight. For these reasons, lithium batteries are increasingly used in the industry.
The lithium rechargeable batteries create electric energy by means of oxidation and reduction reactions during intercalation/deintercalation of lithium ions at the positive and negative electrodes. As the active materials of the positive and negative electrodes of the lithium rechargeable batteries, materials enabling lithium ions to undergo reversible intercalation/deintercalation are used. In addition, an organic electrolyte or a polymer electrolyte is used to fill the space between the positive and negative electrodes.
For the positive electrode active material of the lithium rechargeable batteries, lithium-containing metal oxide is used, including lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), and lithium manganese oxide (LiMnO2). For the negative electrode active material, lithium metal or lithium alloy has been used. When lithium metal is used, however, the batteries may explode as they tend to short-circuit due to the formation of dendrite. Therefore, lithium metal has been replaced by carbon-based materials, including amorphous carbon and crystalline carbon. The lithium rechargeable batteries are manufactured in various shapes including a cylinder type, a square type, and a pouch type.
FIG. 1 is an exploded perspective view showing a conventional lithium rechargeable battery. The lithium rechargeable battery is formed by placing an electrode assembly 12 including first and second electrodes 13, 15 and a separator 14 into a can 10 together with an electrolyte and sealing the top of the can 10 with a cap assembly 20.
The cap assembly 20 includes a cap plate 40, an insulation plate 50, a terminal plate 60, and an electrode terminal 30. The cap assembly 20 seals the can by being coupled to the top opening of the can while being insulated from the electrode assembly 12 by a separate insulation case 70.
The cap plate 40 is made of a metal plate with a size and a shape corresponding to the top opening of the can 10. The cap plate 40 has a centrally located terminal through-hole into which the electrode terminal 30 is inserted. A tubular gasket 35 is coupled to an outer surface of the electrode terminal to provide insulation between the electrode terminal 30 and the cap plate 40 when the electrode terminal 30 is inserted into the terminal through-hole 41. The cap plate 40 has an electrolyte injection hole 42 that is formed on a side thereof with a predetermined size and a safety vent (not shown) on the other side thereof. The safety vent is integrally formed by reducing the sectional thickness of the cap plate 40. After the cap assembly 20 is assembled to the top opening of the can 10, an electrolyte is injected via the electrolyte injection hole 42 which is then sealed by a plug 43.
The electrode terminal 30 is connected to a second electrode tab 17 of the second electrode 15 or to a first electrode tab 16 of the first electrode 13 and acts as a second or first electrode terminal, respectively. Insulation tape 18 is wound around portions through which the first and second electrode tabs 16, 17 protrude from the electrode assembly 12 to avoid a short circuit between the electrodes 13, 15. The first or second electrode may act as a positive or negative electrode.
In the lithium rechargeable battery, the electrolyte is a source for supplying ions and acts as a medium for enabling ions to move so that the battery can undergo reactions efficiently. Electrolyte injection is, therefore, a crucial factor in deciding the performance and life of the battery. Conventional methods for injecting electrolytes include an atmospheric injection method, a centrifugal injection method, and a vacuum injection method.
The vacuum injection method, one of the recently used methods for injection of electrolytes, includes various methods. A typical example thereof includes the following steps: an injection nozzle is attached to the electrolyte injection hole; the inside of the can is evacuated to a vacuum state using an evacuation means of an electrolyte injection apparatus; and a predetermined amount of electrolyte is supplied. Then, the electrolyte is injected into the can by means of the difference in pressure between the can's internal pressure and the atmospheric pressure.
When the electrolyte is injected by the above-mentioned method, however, the cap plate may bend due to the external force applied adjacent to the electrolyte injection hole thereof. If the cap plate is bent in this manner, sealing properties of the can may degrade.